A person should honor his friends just as he would like others to honor him, and he should greatly value the good deeds that a friend does on his behalf.

Rabbi Eliezer says: The honor of your friend should be as precious to you as your own, and [as for you,] do not be easy to anger.

The honor of your friend should be as precious to you as your own; how so? This teaches that just as one is concerned with his honor, so too, he should be concerned with the honor of his friend. And just as a person does not want a bad reputation compromising his honor, so too, a person should not want a bad reputation compromising the honor of his friend.

If you did slight harm to your friend, it should be considered significant in your eyes. If you did significant good for your friend, it should be considered slight in your eyes. By contrast, if your friend did you a minor favor, it should be considered significant in your eyes. If he did significant harm to you, it should be considered slight in your eyes…and be forgiving of affronts to you.

Renounce your desire in favor of the desire of your friend…but renounce your desire and the desire of your friend in favor of the desire of Heaven. (Mishna Avot 2:10; Avot deRabbi Natan, version A, chaps. 15, 41; Derekh Eretz Zuta 1)